Ionic and Molecular Compounds

Types of Chemical Bonds

Ionic and molecular compounds are formed through the transfer or sharing of electrons between atoms, resulting in stable electron arrangements. The two main types of chemical bonds are:

• Ionic Bonds: Formed when valence electrons are transferred from metals to nonmetals, creating ions.

• Covalent Bonds: Formed when atoms of nonmetals share valence electrons, resulting in molecular compounds.

Octet Rule: Atoms tend to lose, gain, or share electrons to achieve eight electrons in their outer shell.

Ions: Formation and Properties

Ions are atoms or groups of atoms with an electrical charge, formed by the loss or gain of electrons.

• Cations: Positive ions formed when atoms lose electrons (typically metals in Groups 1, 2, and 13).

• Anions: Negative ions formed when atoms gain electrons (typically nonmetals in Groups 15, 16, and 17). The name of the anion changes to an "-ide" ending (e.g., chloride).

Ionic Charges from Group Numbers

The group number of representative elements can be used to predict the number of electrons lost or gained:

• Group 1A: Lose 1 electron

• Group 2A: Lose 2 electrons

• Group 3A: Lose 3 electrons

• Group 5A: Gain 3 electrons

• Group 6A: Gain 2 electrons

• Group 7A: Gain 1 electron

Properties and Formulas of Ionic Compounds

Formation and Properties

Ionic compounds are formed when electrons are transferred from metals to nonmetals, resulting in strong attractions and high melting points. They are typically solid at room temperature.

Writing Chemical Formulas

• The formula represents the lowest whole number ratio of ions.

• Subscripts are used to balance charges.

• Always write the cation first, followed by the anion.

• The overall charge of the compound must be zero.

Examples:

• Na+ + Cl- → NaCl

• Mg2+ + 2Cl- → MgCl2

Examples of Ionic Compound Formulas and Names

Naming Ionic Compounds

Simple Ionic Compounds

• Name of the metal (cation) does not change.

• Name of the nonmetal (anion) changes to "-ide" ending.

• Subscripts are not used in the name, only in the formula.

Metals with Variable Charges

Transition elements (except Zn2+, Cd2+, and Ag+) can form multiple cations.

• A Roman numeral is used to indicate the charge (e.g., Iron(II), Iron(III)).

Determining Variable Charge

1. Determine the charge of the cation from the anion.

2. Name the cation with a Roman numeral for its charge.

3. Name the anion with "-ide" ending.

4. Write the cation name first, then the anion.

Example: MnF2 is named manganese(II) fluoride.

Common Elements with Single Charges

Some transition elements only have a single charge: Zn2+, Cd2+, Ag+.

Writing Formulas for Ionic Compounds from Names

1. Identify the cation and its charge.

2. Identify the anion and its charge.

3. Balance the charges.

4. Write the formula, cation first, using subscripts as needed.

Example: Tin(II) chloride → SnCl2

Polyatomic Ions

Definition and Properties

Polyatomic ions are groups of covalently bonded atoms with an overall ionic charge. Most are anions, except NH4+ (ammonium).

• Most polyatomic ions end in "-ate".

• "-ite" is used for ions with one less oxygen.

• "per-" and "hypo-" prefixes indicate more or fewer oxygens, respectively.

Example:

• ClO4-: Perchlorate

• ClO3-: Chlorate

• ClO2-: Chlorite

• ClO-: Hypochlorite

Writing Formulas for Compounds with Polyatomic Ions

• Polyatomic ions combine with ions of opposite charge.

• Balance total positive and negative charges to zero.

• Use parentheses around polyatomic ions when more than one is needed.

• Subscripts for polyatomic ions are placed outside the parentheses.

Naming Compounds with Polyatomic Ions

• Write the cation name first.

• Write the name of the polyatomic ion second.

• Recognition of polyatomic ions is key for correct naming.

Summary Table: Polyatomic Ions

Key Equations

• Charge balance for ionic compounds:

• Example for magnesium chloride:

• Example for sodium sulfide:

Tips for Success

• Always write the cation first in formulas and names.

• Use the correct suffixes for anions and polyatomic ions.

• Balance charges to ensure the compound is neutral.

• Memorize common polyatomic ions and their charges for quick recognition.

Additional info: This guide covers the essential concepts from Chapter 6: Ionic and Molecular Compounds, including bond types, ion formation, naming conventions, and formula writing for both simple and polyatomic ionic compounds. The included tables and images reinforce key points and provide visual context for understanding charge balance and compound structure.